Heretofore, this kind of a sliding member or a seal ring has been used in various kinds of technical fields.
Particularly, the sliding member for sheet-shaped recording material detachment has been used as a separation claw, a separation plate, and the like which detach a sheet-shaped recording material, such as a copying paper and a printing paper, from a roll of a fixing roll or the like in a fixing portion and a development portion of various kinds of image forming devices (hereinafter referred to as a “copying machine”) by an electrophotographic system, such as a copying machine, a laser beam printer, and a printing machine, for example.
As functions of such a separation claw and a separation plate and the like, non-adhesive property which prevents the adhesion of printing toner, shape stability which prevents deformation and breakage of the tip portion of a separation claw and the like, and non-attackability which prevents damages to the roll surface which the most distal end portion thereof contacts, and further, particularly in a separation claw and the like contacting a high-temperature fixing roll, heat resistance which prevents the deformation thereof at a high temperature of about 200 to 250° C. and silent properties during sliding with a roll, and the like are required.
In order to satisfy the above-described demand for the performance as the sliding member for sheet-shaped recording material detachment, such as the separation claw and the separation plate, various proposals have been made. For example, mentioned are a separation claw for a copying machine (Patent Document 1) whose surface non-adhesive property is improved by forming a coat containing a specific fluorocarbon resin, such as tetrafluoroethylene, as the main component on the surface of a molded body of polyimide having a specific structure, a separation claw for copying (Patent Document 2) which is obtained by forming a melt coat of fluorine resin on the surface of a molded body of a resin composite in which a specific proportion of a reinforcing material, such as titanium oxide whiskers or zinc oxide whiskers, is compounded in a polyether ketone resin, a separation claw for copying (Patent Document 3) which is injection molded with a fluorine resin, and the like.
However, in the case of the separation claw and the like in which the melt coat of a fluorine resin is formed on the surface of the heat-resistant resin (hereinafter also referred to as a base material) as described in Patent Documents 1 and 2, one satisfying the above-described demand is obtained. However, there is a problem such that there is a necessity of using an expensive resin, such as polyimide and polyether ketone with high heat resistance, from the viewpoint in a manufacturing process for forming the melt coat of fluorine resin.
Moreover, there are problems such that since the coat is formed on the surface of a molded body of polyimide or the like, by melting a fluorine resin at a high temperature of about 300° C., a coating process has been additionally required and since the energy for heating at a high temperature has been required, additional cost has been required, and the process is not desirable also from the viewpoint of the environmental load.
Furthermore, since the surface hardness of resin, such as polyimide, is generally high, even when a coat is formed on the surface with a fluorine resin, the surface hardness is still high, which causes a risk of damaging the roll surface where the most distal end portion thereof contacts. In addition thereto, when the coat is worn out or the coat is detached due to a certain situation, there arises a problem of considerably damaging the roll surface. Moreover, since the hardness of the surface of the coat is high, silent properties are not so good.
In addition thereto, in a separation claw obtained by forming a coat on the surface of a base material, the quality of the formed coat has influence on the performance of the separation claw. However, the coat forming process is the final process but the process is most likely to cause defects, so that inspection by human beings is required. Therefore, there is a problem such that cost is required for the management aspect of performing the inspection.
In the case of the separation claw for copying which is injection molded with a fluorine resin as described in Patent Document 3, expensive resin, such as polyimide, is not used and a coat is not formed on the surface. Therefore, the separation claw is improved in terms of the cost and the environmental load as compared with the separation claw for copying described in Patent Documents 1 and 2. However, in the case of the separation claw for copying which is injection molded with a fluorine resin, there are problems such that abrasiveness is high and also the rigidity at a high temperature is low.
A seal ring and other sliding members other than the sliding member for sheet-shaped recording material detachment are used for a portion where liquid and gas are required to be sealed or a sliding portion in transport machines, such as automobiles, office machines, a gas compressor, other industrial machines, and the like. For example, a seal ring for use in various pistons for an industrial gas compressor and an automobile and the like are also sliding members. Therefore, the seal ring is required to have low abrasiveness of the seal ring itself and low attackability to a mating member of the seal ring. Furthermore, since the seal ring is also required to have sufficient sealing properties with which the seal ring hardly causes gas leakage, moderate flexibility is required.
However, for example, in an industrial gas compressor, a seal ring for use therein has been increasingly required to also have high mechanical strength with an increase in pressure of compressed gas and an increase in performance of the machine in recent years. Therefore, a currently-used polytetrafluoroethylene (PTFE) resin material containing a filler is limited in the mechanical strength (e.g., tensile strength and bending strength) and cannot meet the demand in some cases.
Thus, in order to satisfy such a request for an increase in pressure, a piston ring and the like in which a material charged with carbon fibers, PTFE, and the like is used for super engineering plastics with high mechanical strength, such as thermoplastic polyimide (TPI) and polyetheretherketone (PEEK) resin, (hereinafter also referred to as “super engineering plastics”) have been proposed (for example, Patent Document 4). However, even when such a material is used, the flexibility is poor, the seal performance is not stable, leakage of gas and the like frequently occurs in the seal ring to be obtained, and the required properties are not obtained.
In order to address the problems, it is said to require a material having high mechanical strength which allows the material to bear high pressure (for example, bending strength (30 MPa or more)) and flexibility which allows the material to satisfy a seal function (for example, bending elastic modulus of 1000 MPa or more and lower than 2000 MPa and bending breaking strain of 4% or more or bending elastic modulus of 2000 MPa or more and lower than 4000 MPa and bending breaking strain of 2% or more).
As a technique for achieving both high strength and flexibility, a method is mentioned which includes mixing a plastic material with higher flexibility with super engineering plastics with high mechanical strength, such as TPI, for alloying. Under the present circumstances, the material having moderate mechanical strength and flexibility described above is not always obtained. For example, even when fluorine resin to be used as a material of a sliding member is employed as the plastic material with high flexibility described above, both the materials do not interact with each other and the materials are simply mixed (which is different from a so-called alloy) and the mixture usually becomes a material which is characterized only by weakness, so that the material is not suitable for practical use. Moreover, depending on the type or the addition amount of resin, the mechanical strength sharply decreases in some cases.
As another method, a piston seal structure has been proposed in which a functional portion having an outer circumferential surface portion constituted by a low friction material, such as PTFE, PI, PEEK, is provided in a piston of a specific structure and one-side gap with the inner circumferential surface portion of a cylinder facing the outer circumferential surface portion is set to 0.03 mm or lower (Patent Document 5). However, under the present circumstances, the piston seal structure cannot sufficiently meet the increase in pressure.